The invention relates to esters, particularly to esters of secondary alcohols and hydroxyacids, processes for preparing such esters by transesterification, and use of the esters in compositions such as lubricating compositions.
Many esters of hydroxyacids, including esters of ricinoleic acid, are described in the literature and/or are commercially available. Castor oil, ergot oil, methyl stearate and methyl ricinoleate are exemplary. Nevertheless, an impediment to preparing additional esters of hydroxyacids, and particularly unsaturated hydroxyacids, is that such esters are susceptible to isomerization and/or alcoholysis in the presence of many reaction conditions that are typically employed to prepare esters. Accordingly, the product ester is in admixture with undesired products. Such undesired products include estolide, which is the ester that forms when the hydroxy group of one fatty acid reacts with the carboxyl group of a different fatty acid molecule. Other undesired products are esters wherein the portion derived from unsaturated fatty acid has a trans rather than cis double bond, and/or the double bond has migrated. Still other undesired products arise upon loss of the hydroxy group to form an additional double bond or where the internal ester is formed.
The following patents, which are exemplary only, describe the preparation of esters containing a hydroxyacid, and specifically ricinoleate esters: U.S. Pat. Nos. 2,486,444; and 1,701,703. The following publications, which are exemplary only, describe the preparation of esters containing the ricinoleate residue: J. American Oil Chemists Society (JAOCS), 67:1375 (1986); JAOCS 73:543 (1996); and JAOCS 73:1385 (1996).
In order to obtain a composition with a high concentration of secondary alcohol ester of a hydroxyacid, it has typically been necessary to perform extensive, and necessarily expensive distillative processes on the product mixture obtained by the ester-forming reaction.
There is a need in the art for a process to prepare esters of hydroxyacids, wherein the alcohol portion of the ester is derived from a secondary alcohol. In particular, there is a need for a process that can be conducted to prepare commercial quantities of secondary alcohol esters of hydroxyacids at a commercially attractive price. The present invention addresses these needs and provides further related advantages as set forth herein.
The present invention provides a transesterification process wherein a secondary alcohol is reacted with an ester of a hydroxyacid, to provide an ester of the secondary alcohol and the hydroxyacid. Thus, in one embodiment, the present invention provides a process that includes reacting an ester of a hydroxyacid with a secondary alcohol in the presence of a transition metal compound, to form a secondary alcohol ester of a hydroxyacid.
In another embodiment, the present invention provides a process for preparing a secondary alcohol ester of a secondary hydroxyacid according to the formula (R4)(R5)CHxe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94R2xe2x80x94CH(OH)xe2x80x94R3. Each of R2, R3, R4 and R5 is independently selected from C1xe2x80x94C22 hydrocarbon groups optionally substituted with one or more of halogen, oxygen and nitrogen. The process includes reacting an ester of a secondary hydroxyacid with a secondary alcohol under transesterification conditions. The transesterification conditions include adding an organometallic compound, preferably an organometallic transesterification catalyst, to one or both of the ester of the secondary hydroxyacid or the secondary alcohol.
The invention provides secondary alcohol esters of hydroxyacids, preferably secondary hydroxyacids, and compositions that include the same. The esters and/or compositions may be included in, and form part of, a lubricating composition, i.e., a composition intended for use in an environment wherein it provides lubrication properties. In one specific embodiment, the invention provides capryl alcohol ricinoleate, and compositions that include this ester, where these compositions may have utility as lubricating compositions.
In another embodiment, the present invention provides a composition that includes at least 50 wt % of a secondary alcohol ester of a secondary hydroxyacid, where the weight percent value is based on the total weight of the composition. The secondary alcohol ester of a secondary hydroxyacid is preferably a secondary alcohol ester of a fatty unsaturated secondary hydroxyacid. The secondary alcohol ester of a secondary fatty unsaturated hydroxyacid is preferably capryl alcohol ricinoleate.
In addition, the invention provides a process of improving the lubricity of a composition, where the process includes incorporating the ester as described above into the composition. In addition, the invention provides a process of modifying the friction properties of a composition, that includes incorporating the ester prepared as described above into the composition. These and related aspects of the invention are described further below.
Generally, the present invention provides a process for preparing a secondary alcohol ester of a hydroxyacid. The process comprises, that is includes, reacting an ester of a hydroxyacid with a secondary alcohol under transesterification conditions. The transesterification conditions include the addition of an organometallic compound to one or both of the reactants, and/or the presence of an organometallic compound in combination with one or both of the reactants, where the organometallic compound is preferably an organometallic catalyst. The product of the transesterification reaction is an ester having the same hydroxyacid component as the starting ester, but the alcohol component is derived from the secondary alcohol.
As used herein, a xe2x80x9ccarboxylic acidxe2x80x9d refers to an organic molecule that includes a carboxylic acid group (xe2x80x94COOH). A carboxylic acid may be generally represented by the formula Raxe2x80x94COOH where Ra refers to an organic moiety.
As used herein, a xe2x80x9chydroxyacidxe2x80x9d refers to an organic molecule that includes a single hydroxy group (xe2x80x94OH) and a single carboxylic acid group (xe2x80x94COOH). Unless otherwise specified, the hydroxy group of the hydroxyacid may be either primary or secondary, where a primary hydroxy group is bonded to a carbon that is, in turn, bonded to one and only one carbon, and a secondary hydroxy group is bonded to a carbon that is, in turn, bonded to two and only two carbons. The hydroxyacid having a primary hydroxy group will be referred to herein as a primary hydroxyacid, while a hydroxyacid having a secondary hydroxy group will be referred to as a secondary hydroxyacid. Hydroxyacids may be generally represented by the formula HOOCxe2x80x94Raxe2x80x94OH where Ra is an organic moiety that links together the IOOCxe2x80x94 and xe2x80x94OH groups. A fatty hydroxyacid has at least 10 carbons, and is a preferred hydroxyacid of the present invention. An unsaturated hydroxyacid includes at least one double bond in addition to hydroxy and carboxylic acid groups. Unsaturated hydroxyacids are a preferred hydroxyacids of the present invention. Unsaturated fatty hydroxyacids have at least 10 carbons and at least one double bond, in addition to hydroxy and carboxylic acid groups, and are another preferred hydroxyacids of the present invention.
As used herein, an xe2x80x9cester of carboxylic acidxe2x80x9d or a xe2x80x9ccarboxylic esterxe2x80x9d refers to an organic molecule wherein the carboxylic acid group (xe2x80x94COOH) of a carboxylic acid (Raxe2x80x94COOH) has been converted to a carboxylic ester moiety (COOxe2x80x94Rb where Rb is an organic moiety). Conceptually, a carboxylic ester can be described as having an acid component and an alcohol component, where in a carboxylic ester of the formula Raxe2x80x94COOxe2x80x94Rb, Raxe2x80x94COOH is the acid component and HOxe2x80x94Rb is the alcohol component. The alcohol component may have either a primary or secondary hydroxy group, so as to be a primary alcohol or a secondary alcohol, respectively. Tertiary alcohols do not work under typical reaction conditions. A primary alcohol ester of a carboxylic acid refers to a carboxylic ester wherein the alcohol component is a primary alcohol. A secondary alcohol ester of a carboxylic acid refers to a carboxylic ester wherein the alcohol component is a secondary alcohol.
As used herein, an xe2x80x9cester of a hydroxyacidxe2x80x9d refers to an organic molecule wherein the carboxylic acid group of a hydroxyacid has been converted to a carboxylic ester group, i.e. molecules of the formula HOxe2x80x94Raxe2x80x94COOxe2x80x94Rb where Ra and Rb are organic moieties. The ester of a hydroxyacid may be a monoester or a polyester, e.g., a diester, triester, etc. For example, when the HOxe2x80x94Rb represents glycerol, and each of three hydroxy groups of glycerol form an ester with a hydroxyacid, the ester of a hydroxyacid may be a triester.
As in esters of a carboxylic acid, an ester of a hydroxyacid may be described as having an acid component and an alcohol component, where, in an ester of a hydroxyacid of the formula HOxe2x80x94Raxe2x80x94COOxe2x80x94Rb, HOxe2x80x94Raxe2x80x94COOH is the hydroxyacid component and HOxe2x80x94Rb is the alcohol component. The hydroxy group of the hydroxyacid component may be a primary or secondary or tertiary hydroxy group, while independently, the hydroxy group of the alcohol component may be a primary or secondary hydroxy group.
The present invention converts two starting materials into a product. The starting materials are a secondary alcohol and an ester of a hydroxyacid. The ester of a hydroxyacid used as a starting material in the inventive process may also be referred to herein as the starting ester. The starting ester may be either a primary alcohol ester of a hydroxyacid, or a secondary alcohol ester of a hydroxyacid. The product is likewise an ester of a hydroxyacid, however, the product ester has an alcohol component that is a secondary alcohol. When the starting ester is a secondary alcohol ester of a hydroxyacid, then the product ester is a different secondary alcohol ester of a hydroxyacid, where the difference lies in that the two esters have different alcohol components.
In a preferred embodiment, the hydroxyacid component of the starting ester and product ester is a secondary hydroxyacid. In this instance, the present invention provides a process for converting an ester (having either a primary or secondary alcohol component) of a secondary hydroxyacid into a secondary ester of a secondary hydroxyacid. In another preferred embodiment, the starting and product esters have a secondary hydroxy group
Thus, the present invention is directed to a transesterification process whereby a first ester of a hydroxyacid is converted to a second ester of the hydroxyacid. The transesterification process includes reacting the first ester of a hydroxyacid with a secondary alcohol in the presence of a transition metal compound. The second ester of the hydroxyacid incorporates the secondary alcohol as the alcohol component of the product ester, and the hydroxyacid component from the starting ester. The present invention provides a process for preparing esters of hydroxyacids wherein the alcohol portion of the ester is a secondary alcohol, and the hydroxy portion of the hydroxyacid may be a secondary alcohol.
Thus, in one aspect, the present invention provides a process that includes reacting an ester of a hydroxyacid with a secondary alcohol in the presence of a transition metal compound, to form a secondary alcohol ester of a hydroxyacid group.
In one embodiment, the ester of a hydroxyacid has the formula 
where each of R1, R2, and R3 are hydrocarbon groups optionally substituted with one or more of halogen, oxygen, and nitrogen. The ester of a hydroxyacid may be viewed as having an alcohol component (R1xe2x80x94OH) and an acid component that is substituted with a secondary hydroxy group (HOxe2x80x94C(xe2x95x90O)xe2x80x94R2xe2x80x94CHOHxe2x80x94R3). The hydroxy group shown in the formula 
is necessarily a secondary hydroxy group, i.e., it is a hydroxy group bonded to a carbon where that carbon is also bonded to two other carbons.
Unless otherwise stated, the identity of a hydrocarbon group at one position is independent of the identity of a hydrocarbon group at a different position. For example, the identity of R1 is independent of the identity of R3, even though each of R1 and R3 is defined as a hydrocarbon group optionally substituted with one or more of halogen, oxygen, and nitrogen. Thus, R1 and R3 may have the same or different structures within the ester of a hydroxyacid as defined above.
As referred to herein, a hydrocarbon group optionally substituted with one or more of halogen, oxygen, and nitrogen refers to a group containing carbon that also contains hydrogen and/or halogen, and may optionally contain one or more of oxygen and nitrogen. Halogen refers to fluorine, chlorine, bromine and iodine, which may be referred to as fluoride, chloride, bromide and iodide, respectively, where preferred halogens are fluorine and chlorine. The group may be linear, branched and/or cyclic, including polycyclic. In addition, the group may be saturated or contain one or more sites of unsaturation, that is, it may contain only single bonds, or it may contain one or more unsaturated bond selected from double, triple and aromatic bonds. The double bond(s) may be between carbons, between carbon and nitrogen, or between carbon and oxygen. The double bond(s) may be cis or trans. The hydrocarbon group may be aliphatic or aromatic. The oxygen(s) and/or nitrogen(s), if present, may form part of a cyclic structure with carbon. All of the hydrogens may be substituted with an equal number of halogens.
In one embodiment, R2 and R3 together have 10 to 30 carbon atoms, and are each unsubstituted hydrocarbon groups. In this embodiment, the hydroxyacid may be referred to as a fatty hydroxyacid, or a fatty acid with hydroxy substitution. The ester of such a hydroxyacid may be referred to as a fatty acid ester. In a preferred embodiment, the hydroxyacid is ricinoleic acid. Ricinoleic acid itself is also known as [Rxe2x80x94(Z)]-12-hydroxy-9-octadecenoic acid and d-12-hydroxyoleic acid. Ricinoleic acid is found naturally in the seeds of Ricinus spp, Euphorbiacea (see, e.g., Merck Index, 12th Ed., page 8382, entry 8378, and references cited therein).
Suitable esters of ricinoleic acid include methyl ricinoleate (i.e., R1 is methyl), castor oil (i.e., R1 is the triglyceride of glycerol), ergot oil, and Guerbet alcohol esters of ricinoleic acid. The methyl ester of ricinoleic acid is described in U.S. Pat. No. 2,486,444. The Guerbet alcohol ester of ricinoleic acid is described in U.S. Pat. No. 5,786,389. Castor oil and ergot oil are each complex mixtures of fatty acids, alkaloids and other compounds. Both castor oil and ergot oil contain suitable esters of ricinoleic, hydroxy stearic and lesquerolic acids, where lesquerolic acid is also known as 14-hydroxy-11-eicosenoic acid. Lesquerolic, ergot, ricinoleic and hydroxy stearic acids are also found naturally in the seeds of Strophanthus, Calendula Officinalis and Strophanthus.
Suitable esters of a hydroxyacid that may be used as a starting material in the present invention are commercially available. In Castor oil, the fatty acid ricinoleic acid is esterified with a polyol, and specifically with glycerol. About 90% of the triglycerides in Castor oil are esters of ricinoleic acid. Castor oil is a commodity chemical available from, for example, CasChem Inc. (Bayonne, N.J.; www.caschem.com), Alnor Oil Company (Valley Stream, N.Y.; www.alnoroil.com), and Jayant Oil Mills (Bombay, India; www.indialog.com/jayant). Other suppliers may be found through the International Castor Oil Association (www.icoa.org). These and other suppliers of castor oil may also supply other esters of ricinoleic acid such as methyl ricinoleate. Many esters of secondary alcohols and fatty hydroxyacids may be used in the present process.
In one embodiment, the starting ester and product esters are each esters of ricinoleic acid. In a further embodiment, the starting ester is castor oil.
The secondary alcohol in the process of the invention has a hydroxy group bonded to a carbon atom, where that carbon atom is bonded to a hydrogen and two other carbons. The secondary alcohol may also be referred to as a hydrocarbon substituted with a secondary,roxy group. In one embodiment, the secondary alcohol is represented by the formula 
where each of R4 and R5 are hydrocarbon groups optionally substituted with one or more of halogen, oxygen and nitrogen. A hydrocarbon group optionally substituted with one or more of halogen, oxygen and nitrogen has been defined above in connection with R1, R2, and R3, and the same definition applies to R4 and R5.
In one embodiment, each of R4 and R5 is independently selected from hydrocarbyl radicals containing from 1 to 22 carbon atoms. In another embodiment, the secondary alcohol is represented by the formula (R4)(R5)CHxe2x80x94OH, where each of R4 and R5 is independently selected from hydrocarbyl radicals containing from 1 to 12 carbon atoms. The secondary alcohol contains a single hydroxy group. Secondary alcohols may be contrasted with primary alcohols, where a primary alcohol has a hydroxy group bonded to a carbon atom, where that carbon atom is bonded to two hydrogens and one carbon. For example, methanol, ethanol and n-propanol are primary alcohols.
Suitable secondary alcohols to employ in the process of the present invention include, without limitation, isopropyl alcohol, 2-butanol, cyclohexanol and capryl alcohol. Capryl alcohol is a preferred secondary alcohol. Suitable secondary alcohols are available from many commercial supply houses, including, for example, Aldrich (Milwaukee, Wis.; www.aldrich.sial.com), and Lancaster Synthesis, Inc. (Windham, N.H.; www.lancaster.co.uk).
The process of the present invention converts one ester of a hydroxyacid into another ester of the same hydroxyacid, in the presence of an organometallic compound. The organometallic compound is preferably a catalyst for the transesterification process. The organometallic compound includes a metal, i. e., includes at least one metal, selected from metals having an atomic number of 13, 21-32, 39-51 and 71-84. In addition, the organometallic compound includes an organic moiety, ie., includes at least one organic moiety. When the organometallic compound includes more than one metal, those metals may be the same or different. When the organometallic compound contains more than one organic moiety, those organic moieties may be the same or different.
Suitable metals that may form part of the organometallic compound include, without limitation, antimony, aluminum, cobalt, manganese, tin, titanium, and zinc. Preferred metals are transition metals, where tin and titanium are exemplary transition metals, and where tin is a preferred metal.
Suitable organometallic compounds are tin salts of organic acids, including, without limitation, tin(II) acetate, tin(II) octoate, tin(II) ethylhexoate and tin(II) laurate. Other suitable compounds are tin(IV) compounds, for example and without limitation, dibutyltin oxide, dibutyltin dichloride, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate and dioctyltin diacetate, where tin(IV) compounds are preferred compounds, and dibutyltin oxide (DTBO) is a preferred tin (IV) compound. Zinc compounds that may be used in the transesterification reaction include, without limitation, zinc acetate and zinc acetylacetate. Manganese compounds include, without limitation, manganese acetate. Still other suitable organometallic compounds are titanium compounds, including, without limitation, titanium acetate and triisopropyl titanate (TPT), where titanium compounds are preferred organometallic compounds, and TPT is a preferred titanium compound.
Such compounds are well known in the chemical literature, and are often referred to as catalysts. These and similar compounds are available from many commercial supply houses including, for example, Aldrich (Milwaukee, Wis.; www.aldrich.sial.com) and Alfa Aesar (Ward Hill, Mass.; www.alfa.com). FASCAT(trademark) organometallic catalysts, available from Elf Atochem North America Inc. (Philadelphia, Pa.; www.elf-atochem.com) as their product designations FASCAT(trademark) stannous oxalate, FASCAT(trademark) 4202 dibutyl tin laurate, and FASCAT(trademark) 4800 alkyl tin salt are preferred catalysts in the invention.
The product of the transesterification process is a secondary alcohol ester of a hydroxyacid and preferably has the formula 
where each of R2, R3, R4 and R5 are hydrocarbon groups optionally substituted with one or more of halogen, oxygen and nitrogen. The definitions of R2, R3, R4 and R5 are the same as provided previously herein.
In certain embodiments of the process of the present invention, each of R1, R2, R3, R4 and R5 is independently selected from C1-C22 hydrocarbon groups; each of R1, R2, R3, R4 and R5 is independently selected from C1-C22 aliphatic groups; the starting and product esters are each esters of ricinoleic acid.
The secondary alcohol esters of hydroxyacids prepared by the present invention wherein R2 contains one or more double bonds are advantageously prepared by the procedures described herein because little or no isomerization of the olefin occurs during transesterification. That is, according to the present invention, a composition comprising an ester of an unsaturated fatty hydroxyacid may be treated with a secondary alcohol and an organometallic compound as defined herein, with a high conversion of the starting ester into the desired product ester. The term xe2x80x9chigh conversionxe2x80x9d refers to the fact that formation of esters from secondary alcohols and unsaturated hydroxyacids typically results in a high level of isomerization and/or loss of the hydroxy group from the fatty acid and/or estolide formation. The term estolide refers to ester formation between two fatty acid molecules, or internal lactone or polyester formation or the loss by dehydration of the secondary hydroxy group. In order for internal esters (lactone) to form from unsaturated carboxylate esters substituted with a secondary hydroxy group, it may be necessary for isomerization of the olefin to first occur. As the present process does not encourage olefin isomerization, the present process is particularly desirable in forming esters from secondary alcohols and unsaturated hydroxyacids.
Mild conditions that do not cause these side-reactions to occur typically employ primary alcohols, e.g., methanol, to form a primary alcohol ester of the hydroxyacid, e.g., methyl ricinoleate. The present invention provides that secondary alcohol esters of hydroxyacids may be formed in high yield by transesterification ester of a secondary hydroxyacid, and preferably a primary alcohol ester of a secondary hydroxyacid. According to the present invention, greater than about 50 wt % of the starting ester may be converted into a product ester. In preferred embodiments, and in preferred order, greater than about 90 wt %, or about 80 wt %, or about 70 wt %, or about 60 wt %, of starting ester is converted into product ester, where these weight percent (wt %) values are based on the total weight of first ester as present in the starting composition.
According to the present invention, a product composition having a molar or weight ratio of secondary alcohol ester of hydroxyacid to estolide in excess of about 1:1, and preferably in excess of about 2:1, and more preferably in excess of about 2.5:1, may be prepared. According to the present invention, a high proportion of the starting ester in the starting material is converted to the desired product ester, with a low proportion of side reaction, e.g., estolide formation, occurring. Accordingly, as referred to herein, the secondary alcohol esters of hydroxyacids preferably do not encompass estolides. Furthermore, none of the secondary alcohol esters of hydroxyacids is a secondary alcohol according to the present invention.
The present invention provides compositions that include the transesterification product of an ester of a hydroxyacid and a secondary alcohol. The composition may additionally include the ester of the hydroxyacid and/or the secondary alcohol, i.e., one or both of the starting materials. In addition, the composition may include estolides or other esters other than the ester formed by transesterification of an ester of a hydroxyacid and a secondary alcohol. Such compositions typically result upon the completion of the transesterification reaction described herein. In one embodiment of the present invention, the product mixture formed by the transesterification process described herein contains at least 50 wt % (preferably at least 60 wt %) secondary alcohol ester of a hydroxyacid, less than 40 wt % (preferably less than 30 wt %) of by-product esters including estolides, and in total, less than 20 wt % (preferably less than 10 wt %) of the ester of the hydroxyacid that was used as the starting material and/or the secondary alcohol starting material, where these weight percent values are based on the total weight of the 3 or 4 mentioned components.
In a preferred embodiment, the present invention provides compositions that contain at least 50 wt % capryl ricinoleate and less than 30 wt % estolides, based on the total weight of capryl ricinoleate, estolides, capryl alcohol, and starting ester of hydroxyacid, where these wt % values may be obtained according to measurements by gel permeation chromatography, as described in the Examples below.
In one aspect of a process of the present invention, the starting ester and the secondary alcohol are combined in a single reaction vessel. Typically, in molar terms, the secondary alcohol is present in at least an equivalent amount, and preferably in a molar excess relative to the amount of starting ester. In this way, all of the starting ester has an opportunity to form a secondary alcohol ester of a hydroxyacid. When castor oil is the starting ester, at least 3 moles of secondary alcohol are typically combined with every one mole of the triglyceride, because 1 mole of triglyceride contains 3 moles of ricinoleate. When methyl ricinoleate or another primary alcohol ester of a hydroxyacid is employed as the starting ester, at least one mole of secondary alcohol is combined with every one mole of methyl ricinoleate. The molar excess of secondary alcohol that may be employed in the present invention is not limiting on the invention. Distillation or other techniques known in the art may readily recover excess or unreacted secondary alcohol.
The amount of organometallic compound employed in the transesterification reaction should be an amount effective to satisfactorily increase the rate of transesterification and/or decrease the formation of by products during the transesterification process. Typically, without any catalyst, the transesterification reaction takes too long to be commercially practical. With the addition of transesterification catalyst, the transesterification reaction rate increases, to a point, beyond which negligible benefit is achieved by adding more catalyst. During the course of the transesterification reaction, the catalyst may become less active, so that additional catalyst may be added during the course of the reaction.
Typically, a catalyst concentration of 0.01 wt % to 5 wt %, based on the total weight of starting ester and secondary alcohol is suitably employed in the beginning stages of the reaction. As stated above, additional catalyst may be added during the course of the reaction. The precise amount of catalyst to include in the reaction mixture may depend on the particular catalyst, or catalysts, that are employed, as well as the particular structures of the staring materials, and of course depends on the desired rate of the transesterification reaction. One of ordinary skill in the art can determine a suitable catalyst concentration without recourse to undue experimentation.
In addition to catalyst, an elevated temperature is typically needed in order to achieve a commercially desirable rate of reaction. Typically, a temperature in the range of 100-250xc2x0 C. is suitable, with temperatures in the range of 150-200xc2x0 C. normally being preferred. The reaction temperature is preferably not in excess of the boiling point of either the starting ester or secondary alcohol or else one or both of these starting materials will distill out of the reaction vessel. In the event it is desired to prepare an ester with a low boiling secondary alcohol, e.g., isopropyl alcohol, it may be desirable to conduct the transesterification reaction under elevated pressure. Devises that may be employed to run a reaction under elevated pressure are well known in the art, see, e.g., Parr Instrument Company (Moline Ill.; www.parrinst.com). In addition, as secondary alcohol boils out of the reaction vessel, additional secondary alcohol may be added to the vessel.
The reaction time will depend, as stated above, on the amount and identity of the transesterification catalyst, the relative amounts of starting ester and secondary alcohol, the structure of the secondary alcohol, and the reaction temperature. As the hydroxy group of the secondary alcohol becomes more hindered, the transesterification reaction rate will decrease. Typically, the transesterification reaction requires several hours to be completed, even at a temperature of 200xc2x0 C., and may require as many as 10-30 hours.
In another embodiment of a process of the present invention, the starting ester and organometallic compound are combined, and then the secondary alcohol is added. In yet another embodiment, the secondary alcohol and organometallic compound are combined, and then the starting ester is added. The order of addition of the starting ester, secondary alcohol and organometallic compound is not critical to the process. However, it is desirable that the reaction mixture contain little or no water. A process wherein potentially wet reactants are added to the reaction vessel, and then the reactants are heated so as to drive off water, prior to addition of the organometallic compound, is preferred if the reactants do, in fact, contain some water. Accordingly, the mixture of starting ester and secondary alcohol preferably includes less than about 10 wt % water, more preferably less than about 5 wt % water, still more preferably less than 2 wt % water, and yet still more preferably less than 1 wt % water, based on the total weight of water (if present), secondary alcohol and starting ester.
The secondary hydroxy esters of the present invention are suitably employed as friction modifiers, lubricity agents, and/or antiwear agents in automotive and/or industrial oil formulations. Suitable formulation may contain mineral oil or other oily substance. The product ester of the invention may be present in the composition at a concentration of about 0.01% to 5%. These compositions are readily prepared by combining the various ingredients and mixing them together. As friction modifiers, the esters of the invention impart desirably low friction coefficients and/or low wear properties to the compositions within which they are placed. As antiwear agents, the esters of the invention impart desirably good antiwear properties to the compositions within which they are placed.
In the Examples that follow, and unless otherwise noted, the chemicals were of reagent grade as obtained from commercial supply houses including Aldrich Chemical Co. (Milwaukee, Wis.) and the like. The diatomaceous earth filter aid was High Flow Super Cell (HFSC). Methyl ricinoleate was from Union Camp Corporation as their product designation CENWAX(trademark) ME methyl ricinoleate, and is now available through Arizona Chemical (Jacksonville, Fla.; www.arizonachemical.com). Capryl alcohol was obtained from Union Camp Corporation, and is now available through Arizona Chemical. FASCAT(trademark) stannous tin based catalysts were obtained from Elf Atochem North America Inc. (Philadelphia, Pa.; www.elf-atochem.com).